We know them best as hugely popular global entertainments, but in the past decade the Harry Potter films have also been phenomenally efficient machines for wealth creation. In this respect, they seem possessed by a kind of alchemy, appropriate for stories about wizardry.

As the eighth and final Potter saga, The Deathly Hallows Part 2, opens this week, it’s clear that author J K Rowling, the prime mover of these films, will feature prominently on “rich lists” for the rest of her life.

The film’s three young stars – Daniel Radcliffe, Emma Watson, Rupert Grint – are routinely described as multi-millionaires, with eight-figure fortunes. And several of the massively talented supporting cast of veteran British actors – Alan Rickman, Maggie Smith, Michael Gambon and the rest – have been known to murmur appreciatively about their “Harry Potter pension”, a generous payment schedule that will keep them comfortably into old age.

But, beyond these famous faces, the Potter films have transformed the lives of dozens of people whose names are unfamiliar to us. These are the unsung heroes of the film business – make-up artists, costume designers, set decorators, camera operators, stunt performers and sound mixers.

Since production began on the first film, The Philosopher’s Stone, in 2000, some of these highly-skilled, behind-the-cameras people who stayed with the Potter franchise in relatively senior positions have quietly become millionaires.

Yet the trickle-down effect from these films has also been enormous. “Think of all the people involved in making them,” says Iain Smith, the veteran British producer (Seven Years in Tibet, Cold Mountain, Children of Men) who now chairs the British Film Commission. “Drivers, junior accountants, painters and decorators. They’ve put money into a lot of people’s pockets, that’s for sure.”

British studios such as Pinewood and Shepperton have been bases for other big Hollywood-backed films, but the Potter franchise, financed by Warner Bros, has been uniquely lucrative for its British cast and crew for several reasons. Firstly, it was conceived on a grand scale. Production-designer genius Stuart Craig was given free rein to create the look of Harry Potter’s world, and of Hogwarts school in particular. No expense was spared in bringing to the screen Craig’s vision, which has endured through eight films.

Thinking big involved hiring big; after the exhausting process of totting up the list of cast-and-crew credits for Deathly Hallows Part 2, you arrive at almost 1,200 names. Thus each film in the series is a major employer.

But perhaps the key factor in their ability to create economic benefit was the promise of steady work over many years. Warners, the film’s British producer David Heyman and his company Heyday Films, realised they had a long-running franchise on their hands, and planned from the outset to adapt all seven of Rowling’s books to film. This gave everyone involved with them a growing sense of financial security.

“There was a sense of extended family that continued employment gives,” says Tanya Seghatchian, a co-producer on the first two Potter movies, and an executive producer on the next two. “In the early days, I remember once walking through Soho thinking, I recognise everyone on the street – they work on our films.”

That’s no exaggeration. Another factor that enhanced the Potter films’ potential for wealth creation was their dependence on visual effects to make Stuart Craig’s vision a reality. Of the 1,200-odd people credited on Deathly Hallows Part 2, an astonishing 714 worked on its visual effects.

The demand for these skilled workers with mysterious job titles (flame artist, VFX data co-ordinator, pipeline lead) has led to a huge boom for post-production companies, many of them in Soho, who supply effects expertise. They remain virtually unknown outside the film industry, but the Potter effect has helped them expand beyond expectations.

As a result, says Smith, “London is now probably the world’s leading centre for visual effects houses. They’ve taken the lion’s share of major work away from Los Angeles. Ten years of Harry Potter has helped them with forward planning. With the creation of the franchise, houses like Framestore and Double Negative have been able to plough capital back into their companies and compete in the international market.”

Smith and Segahatchian (now head of the British Film Institute’s film fund) agree “the HP dividend” goes way beyond merely enriching the film’s cast and crew. “The benefit, in government-speak, is 'strategic,’” says Smith wryly. “These films have given birth to a major new studio in the UK. Without Harry Potter, that would not have happened.”

Indeed. All the films were shot at Leavesden studios in Hertfordshire, built on the site of a former aerodrome. It is now the Warner Bros studio base outside Los Angeles. The company finalised its purchase of Leavesden late last year and plans to invest £100 million in it. Warners is the only Hollywood studio with a UK base.

Impressed by the efficiency with which the early Potter films were produced, Warners have ploughed £1.9 billion into the UK economy in recent years, according to British Film Institute statistics. That includes not only the eight HP movies, but also such titles as The Dark Knight, Sherlock Holmes and Inception.

Then we must factor in those film workers who have received invaluable training on Harry Potter titles. “People who started off as runners, or shadowing someone, have 'passed through Hogwarts’ and gone on to become creatives,” says Seghatchian. “We’ve professionalised the UK film industry in the past 10 years. It now has a far more skilled infrastructure.”

Smith adds that the Potter franchise has done more than make people rich. “It sustains the idea of an indigenous UK industry. The trick is now: What to do? Where to go? Leavesden is a beginning, but we should encourage other [Hollywood] studios to come to Britain.”

Not a bad result, then, for a series of films about a little boy with wizard-like powers. Tomorrow may mark the last time a new Harry Potter film opens in Britain. But “the HP dividend” looks like a gift that will keep on giving for years to come.